The present invention relates to oilfield equipment referred to as rotators for rotating tubing string in a well. More particularly, this invention relates to a tubing rotator with selectable top and bottom connectors for use with a standard spool, so that the tubing rotator may be used in various well applications.
Tubing rotators are used to suspend and rotate a tubing string within the well bore of an oil well. By slowly rotating the tubing string, typical wear occurring within the internal surface of the tubing string by the reciprocating or rotating rods, interior of the string, is distributed over the entire internal surface of the tubing string. As a result, the tubing rotator will prolong the life of the tubing string. Further, rotation of the tubing string relative to the rod string will inhibit buildup of wax or other materials within the tubing string.
Tubing rotators normally are mounted on the flange of a tubing head of a wellhead. In some tubing rotators the tubing string is suspended directly from a rotating output shaft of the tubing rotator. In a second style tubing rotator, the tubing string is suspended from the inner mandrel of a rotatable hanger, which is suspended in the tubing head. In this second style rotator, a hexagonal shaped or other spline shaped output shaft of the tubing rotator engages the inner mandrel to provide rotation of the tubing string. Packing or other seals within the tubing head seal off the well annulus. Tubing heads thus may have a flanged bottom for connecting to the wellhead, and a flanged top for connection to the tubing rotator. Tubing heads alternatively may be threaded at their top end for connection with either a screwed cap or a tubing rotator.
In wellheads that have flanged tubing head tops, the tubing heads are available in many different sizes and pressure ratings. Each size and each pressure rating has different dimensions, bolt size and bolt configuration. Unlike a rotator for threaded engagement with the tubing head, a flanged rotator may be easily positioned rotatably in one of, e.g., 12 equally spaced rotational positions to desirably orient the rotator drive shaft, e.g., worm shaft, with respect to the wellhead and other equipment about the wellhead which functions as a mechanical power source for rotating the drive shaft of the rotator, which then directly or with intermediate components rotates the tubing string.
While a tubing rotation body or spool is attached in a selected manner to the top of the tubing head, the connector at the top of the tubing rotator spool will vary widely in thread type and size, or alternatively in the flange type and pressure rating. In some cases, the spool body or spool of the tubing rotator is integral with either the top connector or the tubing head connector (bottom connector) to the wellhead, and in other cases both the top connector and the tubing head connector are integral with the tubing rotator spool. As a result, a tubing rotator manufacturer must have a wide variety of tubing rotator spools and corresponding internal components in stock to satisfy various applications. U.S. Pat. No. 6,026,898 discloses a one-piece body with a combination flow-T, BOP, and tubing rotator.
Tubing rotators may be driven in a number of ways to function as the source of the rotator drive shaft to rotate the tubing string: (1) they may be driven manually with a ratchet handle; (2) by attaching the ratchet handle to the walking beam with a cable or chain, so that walking beam movement is the power source; (3) by a AC or DC electric motor through a gear reducer; or (4) by a right angle drive attached to the rotating polished rod of a progressing cavity pump, through a flexible drive shaft and gear reducer. In each of these cases, the drive rotates the tubing rotator drive, e.g., worm shaft, which then rotates the tubing string.
With existing tubing rotators, the spool or body of the tubing rotator may thus be different for each configuration, size or pressure rating of the wellhead. As a result, a different mounting bracket for the drive system or power source is required for each style of tubing rotator.
In reciprocating pump jack applications, the lower end of the tubing is often anchored to the casing in tension to prevent vertical movement of the bottom end of the tubing as the pump plunger moves up and down. If the tubing is permitted to move, the effective pump stroke is reduced, thereby reducing pumping efficiency. In order to set the tubing in tension, the top end of the tubing string is lowered below its final landing position when setting the anchor. After the anchor is set, the tubing may then be stretched upward, the lift sub removed, and the hanger attached and landed in the tubing head or the tubing rotator. While the lift sub is being removed and a hanger screwed on, the tubing may be supported in the rig slips. The tubing is over-stretched by the height of the slips plus the distance from the top end of the tubing joint to the bottom of the upset. On shallow wells, the tubing often cannot be stretched this much without yielding the tubing or shearing the shear pins in the anchor.
The disadvantages of the prior art are overcome by the present invention, and an improved tubing rotator is hereinafter disclosed which is easily adaptable for use in various applications.
The tubing rotator may be mounted directly onto either a screwed or a flange type tubing head (wellhead). A tubing rotator spool with a standard main body may be adapted to any wellhead configuration, size or pressure rating by attaching a selected top connector and a selected bottom connector for rigid attachment to the tubing rotator spool. The tubing rotator may also be installed on a well with an anchor without over-stressing the tubing or the anchor.
It is an object of the invention to provide a tubing rotator for attaching to a wellhead for rotating a tubing string, with the rotator including a rotator spool for housing a drive shaft interconnecting a power source and a tubing string for rotating the tubing string, a top connector removably attached at a lower end to an upper end of the rotator spool, and a bottom connector removably attached at an upper end to the lower end of the rotator spool and its lower end to the wellhead. In a preferred embodiment, the rotator spool may include a first set of ports aligned for connecting a selected top connector with the spool housing, and a second set of ports each radially outward from the first set of ports and aligned for connecting another selected top connector with the spool housing.
In another embodiment, it is an object of the invention to provide a tubing rotator wherein the rotator spool may be integral with or removable from a top connector, with the rotator including a bottom connector attached at an upper end to the lower end of the rotator spool and attached at a lower end to the wellhead. The bottom connector includes a retainer sub secured to the spool housing, and a retainer plate removably secured to the retainer sub. The retainer sub may be removably connected to or may be integral with the spool housing.
It is a feature of the present invention that the bottom connector may include threads which tighten in response to torque imparted to rotate the tubing string to prevent unthreading of the connection.
A further feature of the invention is that a locking mechanism may be provided for preventing unthreading of the bottom connector from the rotator spool due to torque imparted to rotate the tubing string.
Yet another feature of the invention is that a double box bushing may be provided within the rotator spool for setting a tension anchor.
A further feature of the invention is that the top connector may include a flow T and/or a BOP.
Another feature of the invention is that a swivel tubing hanger may be used with a locking fitting to prevent the tubing rotator from being improperly installed.
Yet another feature of the invention is that the bottom connector may be attached to the wellhead such that the rotator spool and drive shaft may be oriented in a selected direction relative to the wellhead.
These and further objects, features, and advantages of the present invention will become apparent from the following detailed description, wherein reference is made to figures in the accompanying drawings.